Ocean currents: Tasman Sea a global warming hot spot

August 09, 2015

Canberra (Bernd F. Laeschke - January 2012): The Tasman Sea, a 1,200 mile (2,000 kilometer) body of water between Australia and New Zealand, is developing into a global warming hot spot. Oceanographers have identified a series of hotspots around the world, generated by strengthening wind systems that have driven oceanic currents, including the East Australian Current, polewards beyond their known boundaries.

The hotspots have formed alongside ocean currents that wash the east coast of the major continents and their warming proceeds at a rate far exceeding the average rate of ocean surface warming. "We would expect natural change in the oceans over decades or centuries but change with such elevated sea surface temperatures in a growing number of locations and in a synchronized manner was definitely not expected," said Dr. Wenju Cai, a climate scientist at Australia's Commonwealth Scientific and Industrial Research Organization (CSIRO). "Detecting these changes has been hindered by limited observations but with a combination of multi-national ocean watch systems and computer simulations we have been able to reconstruct an ocean history in which warming over the past century is 2-3 times faster than the global average ocean warming rate."

While the finding has local ecological implications in the region surrounding the hotspots, the major influence is upon the ocean's ability to take up heat and carbon from the atmosphere. In Australia's case, scientists report intensifying east-west winds at high latitudes pushing southward and speeding up the gyre or swirl of currents circulating in the South Pacific, extending from South America to the Australian coast. The resulting changes in ocean circulation patterns have pushed the East Australian Current around 217.5 miles (350 kilometers) further south, with temperatures east of Tasmania as much as two degrees warmer than they were 60 years ago.

The changes are characterized by a combination of currents pushing closer to the Polar Regions and intensify with systematic changes of wind over both hemispheres, attributed to increasing greenhouse gases. The increase of carbon dioxide and other greenhouse gases in the atmosphere has been the major driver of the surface warming of the Earth over the 20th century, Cai said. This trend is projected to continue.

To study the phenomena further, Australian scientists plan to deploy a series of moored ocean sensors across the East Australian Current in March 2013 to observe change season-to-season and year-to-year.

Lead author of the paper first published in the journal Nature Climate Change was Dr. Lixin Wu of the Ocean University of China, with contributing authors from five countries, many of whom are members of the Pacific Ocean Panel working under the auspices of the World Meteorological Organization.

Strengthening wind systems push oceanic currents closer to the Polar Regions and contribute to the development of global warming hotspots around the world.